The present invention relates to a method for decreasing the presence of externally detectable revealing signals, so-called {umlaut over (R)}Ö{umlaut over (S)}, from keyboards, e.g. for computers, where the keyboard is fed with signals, so-called matrix signals, which are detected for detecting activity regarding the keys of the keyboard, whereby said matrix signals are generated by means of a signal device/signal devices.
The invention also regards a device for carrying out the method.
Earlier, attempts have been made to decrease {umlaut over (R)}Ö{umlaut over (S)} from keyboards by a certain encapsulation of the signal devices by means of the keyboard's own encapsulation and by screening of cable devices for the transfer of signals to devices for detection, such as a computer for transformation in a way known per se, to signs, commands or the like, generated by means of the keyboard.
Normally, {umlaut over (R)}Ö{umlaut over (S)} do not originate from said matrix signals, which are usually made of signals of certain, comparatively low basic frequencies, basic tones, but from over-frequencies, harmonics, which are generated at the same time as the basic frequencies and which are externally detectable to a considerably greater extent than the basic frequencies. {umlaut over (R)}Ö{umlaut over (S)} can also come from digital asynchronous serial signals, which comprise information about activity regarding the keys of the keyboard and are the result of a transformation by means of the signal devices for further transfer to devices for detection, such as a computer. Thus, by means of technique used up to now, one has not been able to decrease the externally detectable signals to an acceptable extent.
However, according to the present invention, the presence of externally detectable signals can be decreased to an extraordinary low level or practically be eliminated.
Thus, the present invention relates to a method according to the introductory part of the attached patent claim 1. The method is especially characterized by what is specified in the characterizing part of said patent claim.
The invention further relates to a device according to the introductory part of the attached patent claim 11. The device is especially characterized by what is specified in the characterizing part of the last mentioned patent claim,